Diesel microemulsion biofuels

ABSTRACT

A biofuel can include a diesel fuel, a plant oil, an alcohol viscosity reducer that is either a mixture of a butanol and a C 1 -C 3  alcohol or solely butanol, and a surfactant present at no more than about 1.0% v/v. The biofuel exists as a clear, stable microemulsion at from about −10° C. to about 70° C. with the cloud point and pour point lower than −10° C.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/484,540, filed May 10, 2011, which is incorporated herein by reference.

BACKGROUND

Over the last several decades, energy shortages and rising oil and gasoline prices have elevated the interest in non-petroleum-based renewable fuels. Vegetable oils, particularly non-food feedstock or inedible vegetable oils, have been considered for use as renewable fuels. Candidate vegetable oils have been shown to have similar physical and chemical properties to those of diesel fuel, and thus have comparable performance in diesel engines. However, long-term usage of vegetable oils often leads to engine durability problems. Specifically, such vegetable oil based fuels exhibit poor atomization of the fuel, injector coking and ring sticking due to vegetable oil's higher viscosity than typical diesel fuel. Various studies have reported methods for reducing vegetable oil viscosity in order to overcome these issues. Viscosity reduction protocols include transesterification in which the vegetable oils are chemically converted into their corresponding fatty acid methyl esters or biodiesels. The viscosity of such fatty acid methyl esters is reduced by approximately one order of magnitude. Viscosity of vegetable oils can also be reduced by pyrolysis, in which triglyceride molecules of vegetable oils are thermally cracked into mixtures of methyl esters. Alternatively, viscosity has been reduced by dilution with diesel. However, such blending introduces difficulties with phase separation, stability and energy density.

Factors such as energy content, viscosity, stability and the like can constrain the types of components that are used in fuel mixtures. Many fuel additives substantially reduce energy content or can reduce fuel stability sufficient to make their commercial use unattractive. Various microemulsions have also been studied, although such formulations require high surfactant concentrations in order to maintain phase stability of the fuel. Furthermore, interactions of various fuel additives with other fuel components can increase viscosity above industry acceptable standards. As such, diesel fuel formulations and methods that provide meaningful viable alternatives to diesel-only fuels continue to be sought.

SUMMARY

Stable microemulsion biofuels can be achieved which allow for high fuel stability, low viscosity, and high energy density. Generally, the biofuel can comprise a diesel fuel, a plant oil, less than 1.0% v/v surfactant, and an alcohol viscosity reducer such that the biofuel is a stable microemulsion from about −10° C. to about 70° C. and has a kinematic viscosity less than about 6 cSt at 37.8° C. In one formulation, the diesel biofuel can include a diesel fuel, a plant oil, an alcohol mixture that includes a butanol and a C₁-C₃ alcohol; and a total of surfactant present at no more than about 1.0% v/v. Regardless of the specific components, the diesel biofuel exists as a clear, stable microemulsion at temperatures from about −10° C. to about 70° C. over a period of at least 24 hours. In another aspect, the biofuel exhibits a kinematic viscosity of less than about 6 cSt at 37.8° C. The plant oil can be selected from the group consisting of canola oil, algae oil, jatropha oil, safflower oil, castor oil, linseed oil, tung oil, soy oil, sunflower oil, peanut oil, cottonseed oil, palm oil, coconut oil, rice oil, although other plant oils can be suitable. In a specific example, the plant oil is canola oil. In another example, the C₁-C₃ alcohol is ethanol. The surfactant can be selected from oleyl amine, oleyl alcohol, 1-octanol, ethyl hexyl nitrate, ethyl hexanol, ethylene glycol butyl ether, and mixtures of these surfactants. In particular examples, the surfactant can be 1-octanol, or oleyl amine, or a mixture of these.

In another embodiment, a biofuel can include a diesel fuel, a plant oil, no more than 30% v/v of a butanol as the alcohol viscosity reducer, and no more than about 1.0% v/v of a surfactant mixture. The biofuel exhibits a kinematic viscosity of less than about 6 cSt at 37.8° C. In a particular example, the plant oil and diesel fuel are present at a ratio of from about 1.0:1.0 to about 1.0:3.0. In another example, the surfactant can be 1-octanol, or oleyl amine, or a mixture of these.

A method of making a biofuel can include the mixing of a diesel fuel, a plant oil, an alcohol mixture, and a surfactant at an amount such that the surfactant constitutes less than 1% v/v of the biofuel. The resulting biofuel exists as a clear, stable microemulsion at temperatures from about −10° C. to about 70° C. This biofuel generally exhibits desirable viscosity, pour point, cloud point and stability over a wide variation in temperature. For example, cloud point and pour point can be less than −10° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of fuel consumption in kg/hr at no load and 4 lb-ft load conditions for diesel and selected exemplified biofuel formulations in accordance with specific examples of the present invention.

FIG. 2 is a graph of NOx emissions in ppm at no load and 4 lb-ft load conditions for diesel and selected exemplified biofuel formulations in accordance with specific examples of the present invention.

FIG. 3 is a graph of CO emissions in ppm at no load and 4 lb-ft load conditions for diesel and selected exemplified biofuel formulations in accordance with specific examples of the present invention.

FIG. 4 is a graph of SMPS particulate count at no load and 4 lb-ft load conditions for diesel and selected exemplified biofuel formulations in accordance with specific examples of the present invention.

FIG. 5 is a graph of PM10 results at no load and 4 lb-ft load conditions for diesel and selected exemplified biofuel formulations in accordance with specific examples of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In describing embodiments of the present invention, the following terminology will be used.

The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a surfactant” includes reference to one or more of such component and “mixing” includes one or more of such steps.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “one to six carbons” should be interpreted to include not only the explicitly recited values of one carbon and six carbons, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4 carbons, and sub-ranges such as from one to three, from 2 to 5, and from 3 to 6 carbons, etc. This same principle applies to ranges reciting only one numerical value and should apply regardless of the breadth of the range or the characteristics being described.

As used herein, the term “about” means that dimensions, sizes, formulations, parameters, shapes and other quantities and characteristics are not and need not be exact, but may be approximated and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like and other factors known to those of skill. Further, unless otherwise stated, the term “about” shall expressly include “exactly,” consistent with the discussion above regarding ranges and numerical data.

The term “viscosity” as used herein refers generally to a degree of resistance to flow exhibited by a fluid. There are a number of methods of measuring viscosity recognized in the art, which may be based on different underlying physical variables. As used herein in reference to fuel compositions, “viscosity” refers to kinematic viscosity unless otherwise indicated. Units reported for kinematic viscosity will be cSt.

Microemulsion fuels are clear, low-viscosity, stable dispersions which typically contain a continuous hydrocarbon phase and a discontinuous polar phase. These dispersions can be stabilized by surfactant films and tend to appear isotropic due to the small droplet size (<100 nm) of the equilibrated reverse micelles. Microemulsion fuels have several advantages. For example, microemulsion fuels have been shown to reduce soot formation, NO_(x) and CO emission. Microemulsion fuels can also improve fuel atomization and increase the fuel flash point, which is advantageous for storage. Preparation of these microemulsions can also involve simple mechanical mixing with little or no reaction. As such, implementation and production can be achieved with low capital costs and maintenance.

Diesel-based fuels can be extended by replacing some of the diesel with other components such as plant oils (e.g. vegetable oils). Plant oils are of interest as an alternative to diesel fuel due to their comparable properties and performance to diesel fuel. However, their high viscosity causes engine durability problems after long-term usage. As described herein, vegetable oil viscosity can be reduced by blending the plant oil with diesel fuel in thermodynamically stable mixtures via a microemulsion fuel formulation. In accordance with the present innovation, a method of making a microemulsion biofuel involves the mixing of two immiscible fluids, i.e. a water/short chain alcohol viscosity reducer and a diesel/vegetable oil mixture, to reduce the viscosity of vegetable oil by the aid of surfactants that stabilize the mixture.

In one embodiment, the diesel biofuel can comprise a diesel fuel, a plant oil, an alcohol viscosity reducer, and a very low level of surfactant. The alcohol viscosity reducer can be an alcohol mixture comprising a butanol and a C₁-C₃ alcohol. Alternatively, the alcohol viscosity reducer can be solely a butanol. In one aspect, the stability of the microemulsion biofuels is enhanced and the viscosity is reduced while still maintaining advantageous characteristics by using surfactants to incorporate a short-chain alcohol in the mixtures of diesel and plant oil.

According to the embodiment, the biofuel can include any type of liquid diesel fuel, including petroleum diesel, synthetic diesel and biodiesel. In a particular example, the diesel fuel is a petroleum diesel. The diesel fuel that can be used in the present biofuel is not limited to any particular grade. In a particular example, any grade of diesel fuel available for use in vehicle engines, e.g. grades of No. 1, No. 2, and No. 4 diesel, can be used. In a particular embodiment, the amount of diesel present can be from about 35% v/v to about 99.5% v/v. Synthetic diesel can be formed by conversion of hydrocarbon fuels or natural gas into diesel fuel.

In addition to diesel, the biofuel can comprise an amount of plant oil. The plant oil can be of any kind, without limitation. In particular, the fuel can include one or more plant oils from crop sources that are not used for human consumption. Examples of suitable plant oils include but are not limited to canola oil, algae oil, jatropha oil, safflower oil, castor oil, linseed oil, tung oil, soy oil, sunflower oil, peanut oil, cottonseed oil, palm oil, coconut oil, rice oil, combinations thereof, and transesterification products or pyrolysis products thereof. In a specific example, the plant oil is canola oil.

Plant oil can be included to provide energy content to the biofuel as a replacement for an amount of diesel. The total amount of plant oil, as well as the relative amount of diesel and plant oil, can be selected based on the desired properties of the biofuel. Generally speaking, plant oils tend to be relatively viscous, and increasing the amount of plant oil in a fuel mixture can therefore increase the viscosity of the fuel. In biofuels according to the present technology, however, viscosity is reduced by mixing the diesel/plant oil mixture with one or more short-chain alcohols. In one aspect, this approach allows for the inclusion of greater amounts of plant oils in a biofuel than would otherwise be possible without exceeding practical limits on viscosity for a given type of fuel. In a particular embodiment, the biofuel contains plant oil at from about 20% v/v to about 45% v/v. In another embodiment, plant oil and diesel fuel are present in the biofuel at a ratio of from about 2.0:1.0 to about 1.0:3.0. Viscosity can also be reduced by transesterification or pyrolysis of the plant oil to produce smaller derivative compounds having a lower viscosity.

In accordance with one embodiment, a mixture of at least two alcohols is included in the biofuel. More specifically, this alcohol mixture can comprise two short-chain alcohols. In a particular embodiment, one of the alcohols in the alcohol mixture is a butanol. In one specific example, the butanol in the mixture is sec-butanol. In another specific example, the butanol is n-butanol. Non-limiting examples of butanols can include n-butanol, sec-butanol, isobutanol, tert-butanol, mixtures of these, and the like. In another aspect, the alcohol mixture includes a short chain alcohol having a chain length of C₁ to C₃, such as methanol, ethanol, n-propanol, isopropanol or mixture of these. In a specific example, the short chain alcohol is ethanol. In one particular embodiment, the alcohol mixture used in the biofuel is a mixture of a butanol and ethanol. The alcohols can be anhydrous, or alternatively can include some water. For example, the ethanol used can be 95% ethanol with remainder water. In one aspect, both of the alcohols act as viscosity reducers in the biofuel. In another aspect, the alcohols also contribute to maintenance of the energy content of the biofuel. Therefore, the combination of alcohols selected may provide a balance between these two aspects. For example, the viscosity of ethanol is lower than that of butanol, while butanol has higher energy content than ethanol. Therefore, both ethanol and butanol can be used in the microemulsion biofuel preparation for the purposes of obtaining a desirable viscosity without unduly lowering the energy content of the fuel. As follows from these examples, the biofuel can include a mixture of two, three, or more alcohols to contribute characteristics of viscosity reduction, energy content, or other characteristics to the fuel.

According to another embodiment, a butanol can constitute the sole alcohol in the biofuel. This approach takes advantage of the higher energy content of butanol. In a specific example, the butanol can be present at up to 30% v/v of the fuel. The biofuel according to this embodiment can exhibit a desirable viscosity, e.g. less than 6.0 cSt at 37.8° C. and often from about 1.9 cSt to about 6.0 cSt. In an aspect of this embodiment, somewhat less plant oil may be included in order to maintain this viscosity. For example, in such a biofuel plant oil and diesel fuel can be present at a ratio of from about 1.0:1.0 to about 1.0:3.0.

The total alcohol mixture or individual alcohols can be included in the biofuel in amounts that provide a particular viscosity with respect to the diesel/plant oil makeup present. In an embodiment, the total alcohol mixture is present at from about 12% v/v to about 30% v/v. In another aspect, the relative amounts of individual alcohols in a particular mixture can be selected to provide a given combination of viscosity reduction and energy content. In an embodiment, the alcohol mixture comprises butanol and a C₁-C₃ alcohol at a ratio of from about 2:1 to about 6:1. Ratios close to 1:1 tend to phase separate.

According to the present technology, low-viscosity biofuels can be made by combining diesel, plant oil, and a specific alcohol mixture. In particular, these fuels can include significant amounts of plant oils while exhibiting viscosities that meet accepted requirements for use in diesel engines. For example, fuel viscosity can affect injector lubrication and fuel atomization. That is, fuels with low viscosity may not provide sufficient lubrication for the precision fit of fuel injection pumps or injector plungers, resulting in leakage or increased wear. As such, the diesel biofuel formulation can have a viscosity greater than about 1.9 cSt at 37.8° C. Furthermore, bio-based diesel fuels with high viscosity tend to form larger droplets on injection which can cause poor combustion and increased exhaust smoke and emissions. In a particular aspect, the present biofuels exhibit viscosities of less than 6.0 cSt at 37.8° C.

The biofuels according to the present technology can also be stable microemulsions. These dispersions can be stabilized using surfactants. Surfactants can optionally be excluded from the formulation, for example, if the fuel is used quickly within less than three to four weeks, or less than four days, depending on the specific formulation. However, for commercial operations, plant oil-based fuel microemulsions typically involve the use of significant amounts of surfactant for stability. This requirement can increase the resource costs associated with production of such fuels. Furthermore, the presence of high levels of surfactants can cause maintenance problems in diesel engines. Notably, biofuels according to the present technology exhibit considerable stability while employing very low amounts of surfactant. In one embodiment, the biofuel includes surfactant at no more than about 1.0% v/v but above 0% v/v. In a more specific embodiment, the biofuel can include surfactant at from about 0.5% to about 1.0% v/v, and in some cases no less than about 0.05% v/v surfactant. The present biofuel exhibits considerable stability over a wide range of temperatures. In a particular example, the biofuel is clear and stable at from about −10° C. to about 70° C. Typically, the biofuel can have a cloud point of 40° F. or lower. In another aspect, the biofuel can have a pour point from about 15° F. to about 20° F. One embodiment of the present biofuel has a cloud point and a pour point lower than −10° C.

The biofuel can include any surfactants that are suitable for use in fuels. In particular, hydrophobic surfactants, which tend to form reverse micelles, are indicated for use in this type of microemulsion fuel, and such surfactants are also suitable for use in the present biofuels. Specifically, these fuels can be reverse micellar microemulsion type, in which the continuous phase is the oil (e.g. diesel and canola oil) and the dispersed phase is reverse micellar droplets of water and short chain alcohol. In order to form a reverse micellar microemulsion, the surfactants tend to be hydrophobic since they prefer the hydrophobic oil phase more than hydrophilic surfactants. The selection of surfactant can be based on other contributions to fuel properties. For example, surfactants with fatty acid chains having a sufficiently high heating value can be used in the present biofuels, particularly those having heating values similar to conventional diesel fuel (e.g. 44 MJ/kg). In a specific embodiment, the surfactant is a fatty acid having a heating value of from 40 MJ/kg (such as lauric acid C12) to 46 MJ/kg (such as oleic acid C18). In another aspect, surfactants that enhance the cetane number of fuels, e.g. alkyl amines, can also be used. In a particular embodiment, the surfactant includes at least one of oleyl alcohol, oleyl amine, 1-octanol, ethyl hexyl nitrate, ethyl hexanol, ethylene glycol butyl ether and combinations thereof. In one specific embodiment, the surfactant comprises oleyl amine. In another specific embodiment, the surfactant comprises 1-octanol.

In another embodiment, the biofuel can include a surfactant mixture comprising a surfactant and one or more cosurfactants. In a specific example, the surfactant is a mixture of 1-octanol and oleyl amine. Other non-limiting surfactant combinations include oleyl alcohol and 1-octanol, oleyl amine or oleyl alcohol and one or two of the cosurfactants including 1-octanol, ethyl hexyl nitrate, ethyl hexanol, ethylene glycol butyl ether, and the like. Where a surfactant mixture is used in biofuels according to the present concept, the ratio of constituent surfactant amounts is not particularly limited. Any ratios of surfactants that can provide the viscosity and stability as described herein with the present biofuels, particularly within the total surfactant amounts described herein can be suitable. The ratio employed can be selected based on a desired contribution of individual surfactants to the fuel's properties, such as cetane number or heating value.

The present biofuels can also include a small amount of water. The presence of water in microemulsion fuel can reduce emission of NO and particulates. The water in the fuel may be present by deliberate addition. Alternatively, the biofuel can include water as a byproduct of steps in the production process or be introduced by the addition of particular components. In a particular embodiment, the biofuel can include water at 0.5% v/v or less (i.e. but not zero). Short chain alcohols such as ethanol and methanol can provide a similar effect (i.e. reducing emission of NO_(x), CO and particulates) as water due to their lower combustion temperature than that of diesel fuel.

In accordance with an embodiment, a method of making a stable microemulsion biofuel can comprise mixing together a diesel fuel, a plant oil, an alcohol mixture comprising short chain alcohols, and a surfactant mixture (including cosurfactants) at an amount such that the surfactant constitutes less than 1% v/v of the biofuel. In a particular embodiment, the alcohol mixture includes a butanol and a C₁-C₃ alcohol. Microemulsions typically form spontaneously with slight mixing of these components. Accordingly, the present microemulsion biofuels can be prepared by direct mixing of all of the components using mixing equipment suited for such purposes, e.g. a continuous stirred tank reactor.

EXAMPLES Testing the Effect of Varying Ethanol/Butanol Ratio in Microemulsion Biofuels

Microemulsion biofuels were formulated using the components listed in Table 1 below. Consumer grade canola oil and No. 2 diesel were obtained from local retailers. Ethanol Proof 190 (95% ethanol), sec-butanol, 1-octanol (100% active) and oleyl amine (70% active) purchased from Sigma-Aldrich Corporation, St. Louis, Mo., were used as renewable viscosity reducers. Deionized water was used in all formulations, recognizing a potential modification to surfactant blends from other water sources (such as tap water with hardness).

All fuel ingredients were added together by volume using volumetric cylinders. The 2-butanol and ethanol were the last components to be added in the fuel to minimize evaporation of these components during preparation. The biofuels were then gently hand-shaken at room temperature to obtain clear and homogenous microemulsion upon mixing. Each sample was then stored at a constant temperature ranging from −10° C. to 70° C. in temperature increments of 20° C. (in a freezer or a heating water bath). The biofuels were maintained at each testing temperature for 24 hours before they were observed for any phase separation. For the biofuels without any phase separation at all testing temperatures (Table 1), the viscosity was measured at 37.8° C. and 54.4° C. using a TA Instrument AR550 Rheometer. For each example, viscosity measurement was done in triplicate at 37.8 and 54.4° C. The average value was reported at each temperature. The coefficient of variation was less than 10%. The kinematic viscosity was calculated from the measured dynamic viscosity and the density of the fuel at the corresponding temperatures. The density of the fuel was measured at 37.8 and 54.4° C. using an Anton Paar mPDS 2000 Density Meter.

The cloud point (the temperature at which the fuel begins to thicken and becomes cloudy) and pour points (the temperature at which begins to thicken and no longer pours) of selected biofuels were determined. The standard cloud point for diesel No. 2 in winter weather (November through February) is −10° C. max and in summer weather (March through October) is −4° C. The standard pour point for No. 2 diesel fuel is −17.8° C. and −9.4° C. in winter and summer weathers, respectively. The pour point of the biofuel was measured using a TA Instruments AR550 Rheometer. The cloud point was measured following ASTM D2500, in which the biofuel was observed for the first sign of turbidity and cloudiness in a cooling water bath as the temperature was decreased at intervals of 5° C. The final blends developed were observed to thicken and become cloudy at −10° C. At the other end of the spectrum, phase separation was not observed at temperatures up to 70° C.

The differences between biofuel Examples 1 through 3 shown in Table 1 are that ethanol and butanol were included in three different ratios with a combined concentration of 30%. The kinematic viscosity was measured and was within an acceptable range.

TABLE 1 Composition (in v/v %) of microemulsion fuels in which the ethanol/butanol ratio is varied. Examples 1 2 3 Diesel 35 35 35 Canola oil 35 35 35 Ethanol 95% 0 5 10 Sec-butanol 30 25 20 1-octanol 0.5 0.5 0.5 Oleyl amine 0.35 0.35 0.35 Water 0.15 0.15 0.15 Viscosity (cSt) at 37.8° C. 4.57 4.35 4.12 54.4° C. 3.25 3.12 3.02

Table 1 shows microemulsions that were stable and did not show phase separation after 24 hours between −10° C. and 70° C. It was found that phase separation occurs at an ethanol to butanol ratio of 1:1. As the portion of butanol is increased, for example, at ethanol to butanol ratio of 1:2 and 1:5, no phase separation occurs and the fuel viscosity is still within an acceptable range of 1.9-6 cSt. As the ratio of ethanol to sec-butanol increases, the viscosity of the microemulsion fuel decreases at both testing temperatures (37.8 and 54.4° C.) due to the lower viscosity of ethanol compared to sec-butanol. However, we found that the fuel without ethanol and with 30% of butanol still maintained a desirable fuel viscosity.

Testing the Effect of Varying Total Alcohol Amount

Microemulsion biofuels were formulated by the process of Examples 1 through 3 above, using the components listed in Table 2. In biofuel Examples 4 through 7, ethanol and butanol were included to give three different total alcohol levels, and the kinematic viscosity for each was measured. The ratio of ethanol to sec-butanol was maintained at 1:2.

TABLE 2 Composition (in v/v %) of microemulsion fuels in which total composition of ethanol and butanol is varied. Examples 4 5 6 7 Diesel 35 38 41 44 Canola oil 35 38 41 44 Ethanol 95% 10 8 6 4 Sec-butanol 20 16 12 8 1-octanol 0.5 0.5 0.5 0.5 Oleyl amine 0.35 0.35 0.35 0.35 Water 0.15 0.15 0.15 0.15 Viscosity (cSt) at 37.8° C. 4.13 4.70 5.25 6.81 54.4° C. 3.02 3.24 4.37 5.03

The minimum total composition of ethanol and butanol for the microemulsion fuels to obtain desirable viscosity was determined to be 12 v/v %, as shown in Table 2. The maximum total composition of ethanol and butanol was kept at 30 v/v %. Previous studies showed that higher compositions of ethanol and/or butanol in the fuel have greatly reduced the efficiency of the fuels. The viscosity of the microemulsion fuels increases as the concentration of ethanol and sec-butanol decreases.

Testing the Effect of Varying Total Surfactant Concentration

Microemulsion biofuels were formulated by the process of Examples 1 through 3 above, but using the components listed in Table 3. In biofuel Examples 8 through 11 oleyl amine and 1-octanol were included to give three different total surfactant levels. The 1-octanol/oleyl amine ratio was held at 1.0/0.7 by volume. The 1-octanol has fuel improving effects, while long chain oleyl amine surfactant has a similar heating value to that of diesel and can also act as a cetane enhancer due to the presence of the amine group in the molecule. The amount of water was also varied to keep the volume of water and surfactant/cosurfactant at 2% v/v. The kinematic viscosity for each resulting fuel was measured. As shown in Table 3, as low as only 0.425 v/v % of total surfactant concentration was needed to achieve microemulsion stability.

TABLE 3 Composition (in v/v %) of microemulsion fuels in which total surfactant concentration is varied. Examples 8 9 10 11 Diesel 34 34 35 35 Canola oil 34 34 35 35 Ethanol 95% 5 5 5 5 Sec-butanol 25 25 25 25 1-octanol 1.5 1 0.5 0.25 Oleyl amine 1.05 0.7 0.35 0.175 Water 0.45 0.3 0.15 0.075 Viscosity (cSt) at 37.8° C. 4.31 4.26 4.35 4.29 54.4° C. 3.26 3.23 3.12 3.19

These results demonstrate that the total surfactant concentration has very little effect on the viscosity of the microemulsion biofuels.

Testing the Effect of Varying 1-Octanol/Oleyl Amine Ratio

Microemulsion biofuels were formulated by the process of Examples 1 through 3 above, but using the components listed in Table 4 below. In biofuel Examples 12 through 16, the ratio of 1-octanol/oleyl amine was varied to determine its effect on the stability and viscosity of the microemulsion fuels. Water was added to maintain the ratio between the concentration of total surfactant and water at 1.0%.

TABLE 4 Composition (in v/v %) of microemulsion fuels in which 1-octanol/oleyl amine ratio is varied. Examples 12 13 14 15 16 Diesel 44 44 44 44 44 Canola oil 44 44 44 44 44 Ethanol 95% 4 4 4 4 4 Sec-butanol 8 8 8 8 8 1-octanol 0 0.3 0.5 0.7 1.0 Oleyl amine 0.7 0.49 0.35 0.21 0 Water 0.3 0.21 0.15 0.09 0 Viscosity (cSt) at 37.8° C. 6.97 6.82 6.81 6.61 6.87 54.4° C. 5.15 5.09 5.03 4.98 5.09

The microemulsion fuels were stable at all 1-octanol/oleyl amine ratios. Furthermore, the viscosity of the fuels was not much affected by the variation of the surfactant ratio.

Testing the Effect of Varying Diesel/Canola Oil Ratio

Microemulsion biofuels were formulated by the process of Examples 1 through 3 above, but using the components listed in Table 5 below. In biofuel Examples 17 through 19, the ratio of diesel and canola oil was varied. Other parameters were maintained constant and the kinematic viscosity for each resulting fuel was measured.

TABLE 5 Composition (in v/v %) of microemulsion fuels in which diesel/canola ratio is varied. Examples 17 18 19 Diesel 61 44 31 Canola oil 27 44 57 Ethanol 95% 4 4 4 Sec-butanol 8 8 8 1-octanol 0.5 0.5 0.5 Oleyl amine 0.35 0.35 0.35 Water 0.15 0.15 0.15 Viscosity (cSt) at 37.8° C. 4.58 6.81 9.22 54.4° C. 3.47 5.03 6.38

The microemulsion fuels retained stability over a temperature range from −10° C. to 70° C. However, the viscosity increased as the diesel/canola ratio was decreased.

All of the microemulsion fuel formulations reported in Tables 1 through 5 showed no phase separation within a temperature range of −10° C. to 70° C. over a period of 48 hours. The experimental results show that at the total surfactant/cosurfactant concentration lower than 0.4 v/v %, phase separation occurs. The cloud points and pour points for all of the reported formulations were lower than −10° C.

Testing of Cloud Point and Pour Point of the Biofuel

The cloud point is the temperature at which the fuel begins to thicken and become cloudy. The pour point is the temperature at which the fuel begins to thicken and no longer pours. The cloud point and pour point are important properties of fuels since at the cloud point, some engines fail to run and at the pour point, all engines fail to run. The cloud point and pour point of the biofuels were determined based on the observation of the biofuels to thicken and become cloudy at cold temperature as they are cold properties of the fuels in accordance with ASTM D2500 and ASTM D975, respectively. The microemulsion fuels prepared have cloud points and pour points both lower than −10° C. This meets the accepted requirements for diesel engines (cloud point of 45° F. and pour point of 15-20° F.). The ability of biofuels to function at low temperatures is a consideration in regions with seasonal climatic extremes.

Testing of Performance of the Biofuels in an Instrumented Diesel Engine

From the matrix of blends described above, biofuels with a kinematic viscosity less than 6.0 cSt at 37.8° C. were run in an instrumented Kubota 482 cc diesel engine at the University of Utah. No. 2 diesel fuel was also run under the same operating conditions for baseline performance and emission comparisons. Two engine conditions were tested: an idle condition and a scenario representing running at high load conditions. Fuel was gravity fed to the engine from a platform with a digital scale so that fuel consumption could be gravimetrically determined. Exhaust from this engine was sent directly to a Model 300 California Analytical CO/CO₂ analyzer and a Thermo Electron Chemiluminescence NOx analyzer and gas concentration (in ppm) was continuously recorded. Exhaust gas was also sent to an eductor and a dilution manifold from which samples were drawn and analyzed by a TSI DustTrak PM 10 monitor and a TSI Scanning Mobility Particle Sizer (SMPS) to determine the exhausted particle size distribution and concentration. The DustTrak PM 10 provides a mass-based measurement of particulate matter (PM) with a diameter of 10 microns or less (PM 10) while the SMPS senses particle sizes ranging from 14 to 720 nm.

The mass of the fuel was recorded before and after each test run, yielding average fuel consumption. Before each test, the siphon line was drained and the new fuel to be tested was flushed through the functioning engine for ˜5 minutes. The engine was set at two conditions for each fuel: no load at 1500 rpm and 4 ft-lb at 2200 rpm. At each loading condition, the engine was run for 30 minutes for each fuel after the five-minute flushing period. All gas and particle data were continuously recorded.

FIG. 1 shows the fuel consumption for diesel (baseline) and for selected microemulsion fuels at the two engine conditions. The ordinate designates consumption in kg/hour and the abscissa indicates the microemulsion formulation, as designated in Tables 1 through 5. As anticipated, for all fuels the fuel consumption is much lower at no-load conditions than under high-load conditions. Microemulsion fuel consumption is universally higher than diesel at both conditions, specifically from about 9-23% and 6-20% higher at no-load and high-load conditions, respectively. This is due to the presence of short chain alcohols, which have much lower energy content than diesel fuel, in the microemulsion fuels.

Microemulsion fuel formulations 3, 4, 5 and 6 have a progressively decreasing concentration of ethanol and sec-butanol (see Table 2). As the total ethanol and sec-butanol concentration decreases from 30% (Formulation 3) to 12% (Formulation 6), fuel consumption decreases. Microemulsion fuel formulations 6, 14 and 15 (61/26 to 44/44 to 31/57, respectively) have varying ratios of diesel to canola oil (see Table 5). At no-load conditions, the fuel consumption was nominally unaffected by the studied diesel/canola oil ratio. However, under high-load condition, as the diesel/canola oil decreases from 61/26 to 44/44 to 31/57, fuel consumption increases from 3.6 to 3.8 to 4.0 kg/hr (diesel was 3.4 kg/hour). The lower cetane number and the lower heat content of canola oil, as compared to diesel fuel cause this fuel consumption to increase with an increasing amount of canola oil in the microemulsion fuel.

The NOx emissions were also measured. These are compared in FIG. 2. Similar trends in the NOx emission were observed under no-load and high-load conditions. Under no-load condition, NOx emission from all of the microemulsion fuels did not exceed of the baseline for No. 2 diesel. Under high-load condition, emission relative to diesel was variable—some higher and some lower. As the total concentration of ethanol and sec-butanol decreases from 30% in Formulation 3 to 12% in Formulation 6, NOx emissions increase. For Formulations 6, 10 and 13 (see Table 4), as the ratio of 1-octanol to oleyl amine increases, NOx emissions decrease slightly. It was observed that NOx emissions were not affected by varying ratios of diesel and canola oil in the fuel (Formulations 6, 14 and 15). From these limited data, it appears that NOx emission is reduced by replacing a portion of the diesel by short chain alcohols (which also act as viscosity reducers) and by increasing the concentration of cetane number improver in the fuel.

FIG. 3 shows the CO emissions from No. 2 diesel fuel and the tested microemulsion fuels. CO emissions from the microemulsion fuels are significantly larger than for the diesel at no-load conditions. CO emissions only slightly increase or remain the same at high-load conditions. For the microemulsion fuels with a 30% total ethanol/sec-butanol concentration (Formulations 1, 2, 3 and 9), carbon monoxide emissions are higher than for the other microemulsion fuels which have lower concentrations of ethanol and sec-butanol. CO emissions decreases more obviously as the ethanol and sec-butanol concentrations decrease under no-load running conditions (Formulations 3, 4, 5 and 6, see Table 2).

Particle emissions from diesel combustion exhaust constitute some fraction of the air pollution that has been implicated in human heart and lung damage. The exposure to PM 10 (particles with a diameter of 10 μm or less) can pose major concern for human health. To assess this risk, particle emissions (FIG. 4) and PM 10 emissions (FIG. 5) were measured and compared for the diesel and microemulsion fuels used in the engine tests. FIG. 4 shows the recorded particle counts 14 to 720 nm in the exhaust from engine tests. As the concentration of ethanol and sec-butanol decreases to 24% and less (the remaining microemulsion fuels), the particle count measured for the microemulsion fuels significantly decreases. The particulate matter reduces as ethanol and sec-butanol are added because of their oxygen content of ethanol and sec-butanol. Most of the microemulsion fuels have PM 10 emission that meets the EPA's health-based national air quality standard of 150 μg/m³ daily concentration.

For the idle conditions in this particular laboratory-scale engine, the fuel consumption of the biofuels is higher than that of No. 2 diesel fuel by about 7.5% to about 23%. The NO_(x) emission is lowered by up to about 37%, although it increased for those with 30% alcohol. The CO emission is higher for all of the biofuels. Compared to No. 2 diesel fuel, the biofuels emitted particulates with a higher total concentration than No. 2 diesel fuel alone, but PM 10 (particulate matters with diameter of 10 micron or less) concentration of 20 to 74% lower depending on formulations.

For running at high load conditions (i.e. 4 lb-ft at 2200 rpm) in the particular instrumented motor, biofuel consumption is higher than that of No. 2 diesel fuel by about 5.6% to about 20% while the NO_(x) and CO emissions are lowered by up to about 16% and 6%, respectively. Compared to No. 2 diesel fuel, the biofuels with alcohol concentration of 24% or less emit particulates with concentration of 23 to 67% lower and PM 10 concentration of 36 to 93% lower for all of the biofuels.

While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below. 

What is claimed is:
 1. A biofuel, comprising: a diesel fuel; a plant oil or derivative thereof; an alcohol viscosity reducer; and a surfactant present at no more than about 1.0% v/v, wherein the biofuel exists as a clear, stable microemulsion at temperatures from about −10° C. to about 70° C. and has a kinematic viscosity of less than about 6 cSt at 37.8° C.
 2. The biofuel of claim 1, wherein the plant oil is selected from the group consisting of canola oil, algae oil, jatropha oil, safflower oil, castor oil, linseed oil, tung oil, soy oil, sunflower oil, peanut oil, cottonseed oil, palm oil, coconut oil, rice oil, transesterification product thereof, pyrolysis product thereof, and combinations thereof.
 3. The biofuel of claim 2, wherein the plant oil is canola oil.
 4. The biofuel of claim 1, wherein the alcohol viscosity reducer is an alcohol mixture comprising a butanol and a C₁-C₃ alcohol.
 5. The biofuel of claim 4, wherein the C₁-C₃ alcohol is ethanol.
 6. The biofuel of claim 4, wherein the butanol is sec-butanol.
 5. The biofuel of claim 4, wherein the butanol is n-butanol.
 8. The biofuel of claim 4, wherein the alcohol mixture is present at from about 12% v/v to about 30% v/v.
 6. The biofuel of claim 4, wherein the butanol and the C₁-C₃ alcohol are present at a ratio of from about 2:1 to about 6:1.
 7. The biofuel of claim 4, wherein the butanol is present at up to 30% v/v.
 11. The biofuel of claim 1, wherein the alcohol viscosity reducer consists essentially of a butanol present at no more than 30% v/v.
 12. The biofuel of claim 1, wherein the surfactant is a fatty acid having a heating value of from 40 MJ/kg to 46 MJ/kg.
 13. The biofuel of claim 1, wherein the surfactant is selected from the group consisting of oleyl amine, oleyl alcohol, 1-octanol, ethyl hexyl nitrate, ethyl hexanol, ethylene glycol butyl ether, and combinations thereof.
 14. The biofuel of claim 13, wherein the surfactant comprises 1-octanol.
 15. The biofuel of claim 13, wherein the surfactant comprises oleyl amine.
 16. The biofuel of claim 1, wherein the surfactant is present at from about 0.5% v/v to about 1.0% v/v.
 8. The biofuel of claim 1, wherein the diesel fuel is present at from about 35% v/v to about 99.5% v/v.
 9. The biofuel of claim 1, wherein the plant oil and diesel fuel are present at a ratio of from about 1.0:1.0 to about 1.0:3.0.
 10. The biofuel of claim 1, further comprising water at no more than about 0.5% v/v but greater than 0% v/v.
 20. A method of making a biofuel, comprising mixing a diesel fuel, a plant oil, an alcohol viscosity reducer, and a surfactant at an amount such that the surfactant constitutes less than 1% v/v of the biofuel, where the biofuel exists as a clear, stable microemulsion at from about −10° C. to about 70° C. 